1. Field of the Invention
This invention relates mainly to a root canal measuring apparatus, and more particularly to an improved root canal measuring apparatus using a tooth electrode only.
2. Description of the Prior Art
In root canal treatments, it is required to correctly know the length of a root canal, or the length from the incisal edge of a tooth or the edge of a tooth cavity through the root canal to the stricture portion of the root apex (hereinafter referred to as a root canal length).
FIG. 1 is a schematic cross-sectional view showing a construction of a tooth, in which reference numeral 1 designates a tooth, 2 a pulp, 3 a root canal in which the pulp 2 is housed and 4 a cavity bored in the tooth material reaching the root canal 3. Further, 5 denotes a alveolar bone, 6 a gingiva, and 7 a root canal membrane.
For example, in the root canal treatment, the root canal 3 surrounded by a necrosis dentin has no spontaneous protective force or spontaneous treatment capacity, and hence treatments of removing damages in periodontal tissue, such as the removal of infected part or protection of re-infection, are required, or root canal widening or root canal filling treatments become necessary. In this case, however, the treatments of periodontal tissue such as the periodontal membrane 7 spaced from the apical stricture portion 3A at the apex of the root canal 3 are not desirable because the above treatments result in the obstruction of the spontaneous protective force or spontaneous treatment capacity present in the periodontal tissue.
Further, in extirpation of the pulp, the pulp 2 is desired to be cut at the apical stricture portion 3A in which the circulation of blood necessary for hurt treatment can be expected from a viewpoint of the hurt treatment after the extirpation of pulp. For this reason, it is required to measure the position of the apical stricture portion 3A, or the root canal length l.
As described above, in the dental treatment, the measurement of the root canal length l is indispensable. As a prior art measuring method of root canal lengths, there have been proposed a measuring method using X-ray photography, a method of measuring root canal length by feeling of operator's fingers or patient's complain of pain when the tip of a needle inserted into the root canal 3 has reached the apical stricture portion 3A, and the like. However, when using the X-ray photography, it is difficult to correctly arrange an X-ray film at a predetermined position inside a narrow mouth. For the above reason, it is quite difficult to achieve a correct measurement of the root canal length. Also, its operation is complicated, and an influence of X-ray onto a human body will come into question. Further, in the case of using the feeling of operator's fingers and the patient's complain of pain, their experiences are individually different in a great range and hence correct measurements of root canal length are carried out with difficulty.
In order to remove the above defects, a method of electrically measuring root canal length has recently been proposed and spotlighted. This apparatus utilizes characteristics such that an electric resistance between an oral mucous membrane 9 and a periodontal membrane 7 always exhibits a constant value at any portion of the periodontal membrane 7 as mentioned previously. It is experimentally noticed that this resistance value is about 6 to 6.5 K.OMEGA. which is quite lower than a resistance value of the tooth 1 itself. This apparatus is constructed as shown in FIG. 2 by way of example.
In FIG. 2, a tooth electrode, for example, a reamer 11 is connected through a clip 25 and a current detecting resistor 22 to one end of an oscillating circuit 21 of a low frequency, for example, 50 to 3000 Hz, while a saliva removing pipe 12 serving as an oral mucous membrane electrode is connected through a clip 26 to the other end of the oscillating circuit 21. An amplifier 23 is connected across the resistor 22 and the output end of the amplifier 23 is connected to a meter 24.
With the above mentioned apparatus shown in FIG. 2, when the reamer 11 is inserted into the root canal 3 but its tip is not reached to the periodontal membrane 7, a resistance between the reamer 11 and the saliva removing pipe 12 is relatively large and a current flowing through the resistor 22 is small, so that the meter 24 shows a small deflection. However, as the tip of the reamer 11 approaches the periodontal membrane 7, the deflection of the meter 24 becomes gradually large. When the tip of the reamer 11 has reached the periodontal membrane 7, the resistance between the reamer 11 and the pipe 12 becomes a substantially constant value in a range from 6 to 6.5 K.OMEGA. and the deflection of the meter 24 becomes large. For example, when the full scale of the meter 24 is selected as 50 .mu.A, the pointer of the meter 24 will indicate a value in a range from 40 to 42 .mu.A.
Accordingly, in order to measure the root canal length l, the reamer 11 is first gently inserted into the root canal 3. Then, when the meter 24 shows a constant value, it means that the tip of the reamer 11 has reached the periodontal membrane 7. Therefore, at that time the reamer 11 is put thereon with a proper mark before the reamer 11 is drawn out. Thereafter, the length of the reamer 11 between the tip and the mark is measured to obtain the root canal length l necessary for treatment. In a practical case, however, zero-point adjustment and full-scale adjustment of the meter 24 are required to be carried out before measuring.
Thus, according to this measuring apparatus, the root canal length l can be simply and precisely measured. However, the apparatus is required to use the oral mucous membrane electrode, or the saliva removing pipe 12, and hence the root canal length l can not be measured without using the above pipe 12. In addition, the pipe 12 must be made of metal as an electrode in this case. Recently, however, saliva removing pipes made of resin such as vinyl are being pervaded due to flexibility, light weight, easiness in use, and the like. Accordingly, with the prior art apparatus, when the saliva removing pipe made of resin is used, additional oral mucous membrane electrode made of metal must be inserted in the mouth, so that an operating space becomes narrow and the additional electrode acts to obstruct the operation. Further, even in the case of using the saliva removing pipe made of metal, the clip 26 must be connected to the pipe and hence it causes inconvenience in handling.